Systems and methods related to linear load modulated power amplifiers

ABSTRACT

Systems and methods related to linear load modulated power amplifiers. A power amplifier (PA) system can include an input circuit configured to receive a radio-frequency (RF) signal and split the RF signal into a first portion and a second portion. The PA system can further include a Doherty amplifier circuit including a carrier amplifier coupled to the input circuit to receive the first portion and a peaking amplifier coupled to the input circuit to receive the second portion. The first portion and the second portion can have different phases and/or different powers. The PA system can further include an output circuit coupled to the Doherty amplifier circuit. The output circuit can be configured to combine outputs of the carrier amplifier and the peaking amplifier to yield an amplified RF signal.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to U.S. Provisional Application No.61/992,844 filed May 13, 2014, entitled SYSTEMS AND METHODS RELATED TOLINEAR LOAD MODULATED POWER AMPLIFIERS, the disclosure of which ishereby expressly incorporated by reference herein in its entirety.

BACKGROUND

1. Field

The present disclosure generally relates to radio-frequency (RF) poweramplifiers (PAs).

2. Description of the Related Art

Traditionally, it has been widely believed that the Doherty PA was notsuitable for linear PA applications in handsets due to the size,complexity, and non-linear behavior. In fact, in base stationapplications, predistortion linearizers are typically used with DohertyPAs to meet linearity requirements. As described herein, issues such assize, complexity, and linearity associated with Doherty PAs can beaddressed appropriately.

SUMMARY

In accordance with some implementations, the present disclosure relatesto a power amplifier (PA) system including an input circuit configuredto receive a radio-frequency (RF) signal and split the RF signal into afirst portion and a second portion. The PA system further includes aDoherty amplifier circuit including a carrier amplifier coupled to theinput circuit to receive the first portion and a peaking amplifiercoupled to the input circuit to receive the second portion. The firstportion and the second portion having different phases and differentpowers. The PA system further includes an output circuit coupled to theDoherty amplifier circuit. The output circuit is configured to combineoutputs of the carrier amplifier and the peaking amplifier to yield anamplified RF signal.

In some embodiments, the input circuit can include a phase-shifterconfigured to cause the first portion and the second portion to havedifferent phases. In some embodiments, the phase-shifter and peakingamplifier can be implemented in a peaking amplification path. In someembodiments, the first portion and second portion can be out-of-phase bybetween 10 degrees and 20 degrees. In some embodiments, the differentphases can reduce at least one of AM/AM distortion or AM/PM distortionas compared to equal phases.

In some embodiments, the input circuit can include an attenuatorconfigured to cause the first portion and the second portion to havedifferent powers. In some embodiments, the attenuator and the carrieramplifier can be implemented in a carrier amplification path. In someembodiments, the different powers can reduce at least one of AM/AMdistortion or AM/PM distortion as compared to equal powers.

In some embodiments, the input circuit can include a pre-driveramplifier.

In some embodiments, the peaking amplifier includes a driver stageconfigured to operate in a first biasing mode and an output stageconfigured to operate in a first biasing mode. In some embodiments, thefirst biasing mode is a Class B biasing mode. In some embodiments, theClass B biasing mode increases the PAE of the peaking amplifier ascompared to a Class AB biasing mode. In some embodiments, the carrieramplifier includes a driver stage configured to operate in a secondbiasing mode. In some embodiments, the second biasing mode is a Class ABbiasing mode. In some embodiments, the carrier amplifier furtherincludes an output stage configured to operate in the first biasingmode. In some embodiments, the carrier amplifier further includes anoutput stage configured to operate in the second biasing mode.

In some implementations, the present disclosure relates to a poweramplifier (PA) module. The PA module includes a packaging substrateconfigured to receive a plurality of components and a PA systemimplemented on the packaging substrate. The PA system includes an inputcircuit configured to receive a radio-frequency (RF) signal and splitthe RF signal into a first portion and a second portion. The PA systemfurther includes a Doherty amplifier circuit including a carrieramplifier coupled to the input circuit to receive the first portion anda peaking amplifier coupled to the input circuit to receive the secondportion. The first portion and the second portion have different phasesand different powers. The PA system further includes an output circuitcoupled to the Doherty amplifier circuit. The output circuit isconfigured to combine outputs of the carrier amplifier and the peakingamplifier to yield an amplified RF signal.

In some embodiments, at least one of the input circuit or the outputcircuit can be implemented as an integrated passive device. In someembodiments, at least one of the input circuit or the output circuit canbe implemented on a single GaAs die.

In some implementations, the present disclosure relates to a wirelessdevice. The wireless device includes a transceiver configured togenerate a radio-frequency (RF) signal. The wireless device includes apower amplifier (PA) module in communication with the transceiver. ThePA module includes an input circuit configured to receive the RF signaland split the RF signal into a first portion and a second portion. ThePA module includes a Doherty amplifier circuit including a carrieramplifier coupled to the input circuit to receive the first portion anda peaking amplifier coupled to the input circuit to receive the secondportion. The first portion and the second portion have different phasesand different powers. The PA module includes an output circuit coupledto the Doherty amplifier circuit. The output circuit is configured tocombine outputs of the carrier amplifier and the peaking amplifier toyield an amplified RF signal. The wireless device further includes anantenna in communication with the PA module. The antenna is configuredto facilitate transmission of the amplified RF signal.

In some implementations, the present disclosure relates to a method foramplifying a radio-frequency (RF) signal. The method includes providinga Doherty amplifier circuit having a carrier amplification path and apeaking amplification path, receiving an RF signal, splitting the RFsignal into a first portion and a second portion, the first portionprovided to the carrier amplification path, the second portion providedto the peaking amplification path, the first portion and the secondportion having different phases and different powers, and combining anoutput of the carrier amplification path and an output of the peakingamplification path to yield an amplified RF signal.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the inventions have been described herein. It isto be understood that not necessarily all such advantages may beachieved in accordance with any particular embodiment of the invention.Thus, the invention may be embodied or carried out in a manner thatachieves or optimizes one advantage or group of advantages as taughtherein without necessarily achieving other advantages as may be taughtor suggested herein.

The present disclosure relates to U.S. patent application Ser. No.______ [Attorney Docket 75900-50074US], entitled SYSTEMS AND METHODSRELATED TO LINEAR AND EFFICIENT BROADBAND POWER AMPLIFIERS, and U.S.patent application Ser. No. ______ [Attorney Docket 75900-50115US],entitled CIRCUITS, DEVICES AND METHODS RELATED TO COMBINERS FOR DOHERTYPOWER AMPLIFIERS, filed on even date herewith and hereby incorporated byreference herein in their entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example architecture of a power amplifier (PA) havingone or more features as described herein.

FIG. 2 shows an example of a combiner circuit for a Doherty PA.

FIG. 3 shows an example of a splitter circuit for a Doherty PA.

FIG. 4 shows an example of a power splitter that can be utilized as thedivider of FIG. 1.

FIG. 5 shows another example of a power splitter that can be utilized asthe divider of FIG. 1.

FIG. 6 shows an example of a combiner that can be utilized as thecombiner of FIG. 1.

FIG. 7 shows another example of a combiner that can be utilized as thecombiner of FIG. 1.

FIG. 8 shows an example of a low headroom Class AB bias circuit.

FIG. 9 shows an example of a low headroom Class B bias circuit.

FIG. 10 shows an example of a beneficial effect of utilizing a Class Bbiasing of the driver stage for a peaking amplifier.

FIG. 11 shows another example of a beneficial effect of utilizing aClass B biasing of the driver stage for a peaking amplifier.

FIG. 12 shows an example of linearization effect that can be obtained byintroducing a phase shift between the RF signals associated with carrieramplification and peaking amplification.

FIG. 13 shows an example of linearization effect that can be obtained byintroducing an uneven power split between the RF signals associated withcarrier amplification and peaking amplification.

FIG. 14 shows an example of combined linearization effect that can beobtained by a combination of the phase shift and uneven power split.

FIG. 15 shows example plots of power-added efficiency (PAE) and adjacentchannel power (ACP) at various operating frequencies for a front-endmodule (FEM).

FIG. 16 depicts a wireless device having one or more features describedherein.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The headings provided herein, if any, are for convenience only and donot necessarily affect the scope or meaning of the claimed invention.

Disclosed are various examples related to Doherty power amplifier (PA)applications, such as those for high peak to average power ratio (PAPR)4G modulation signals used in 3G and 4G handset applications. In someembodiments, by utilizing the Doherty approach over other designs, up to10% higher peak power added efficiency (PAE) levels can be achieved forthe same adjacent power level ratio (ACLR) levels. Such PAE performancecan match that of an envelope tracking (ET) PA for much less overallsystem complexity.

Traditionally, it has been widely believed that the Doherty PA was notsuitable for linear PA applications in handsets due to the size,complexity, and non-linear behavior. In fact, in base stationapplications, predistortion linearizers are typically used with DohertyPAs to meet linearity requirements. As described herein, issues such assize, complexity, and linearity associated with Doherty PAs can beaddressed appropriately.

FIG. 1 shows an example architecture of a PA 100 having one or morefeatures as described herein. The architecture shown is a Doherty PAarchitecture. Although the various examples are described in the contextof such a Doherty PA architecture, it will be understood that one ormore features of the present disclosure can also be implemented in othertypes of PA systems.

The example PA 100 is shown to include an input port (RF_IN) forreceiving an RF signal to be amplified. Such an input RF signal can bepartially amplified by a pre-driver amplifier 102 before being dividedinto a carrier amplification path 110 and a peaking amplification path130. Such a division can be achieved by a divider 104. Examples relatedto the divider 104 (also referred to herein as a splitter or a powersplitter) are described herein in greater detail.

In FIG. 1, the carrier amplification path 110 is shown to include anattenuator 112 and amplification stages collectively indicated as 114.The amplification stages 114 are shown to include a driver stage 116 andan output stage 120. The driver stage 116 is shown to be biased by abias circuit 118, and the output stage 120 is shown to be biased by abias circuit 122. In some embodiments, there may be more or less numberof amplification stages. In various examples described herein, theamplification stages 114 are sometimes described as an amplifier;however, it will be understood that such an amplifier can include one ormore stages.

In FIG. 1, the peaking amplification path 130 is shown to include phaseshifting circuit 132 and amplification stages collectively indicated as134. The amplification stages 134 are shown to include a driver stage136 and an output stage 140. The driver stage 136 is shown to be biasedby a bias circuit 138, and the output stage 140 is shown to be biased bya bias circuit 142. In some embodiments, there may be more or lessnumber of amplification stages. In various examples described herein,the amplification stages 134 are sometimes described as an amplifier;however, it will be understood that such an amplifier can include one ormore stages.

FIG. 1 further shows that the carrier amplification path 110 and thepeaking amplification path 130 can be combined by a combiner 144 so asto yield an amplified RF signal at an output port (RF_OUT). Examplesrelated to the combiner 144 are described herein in greater detail.

FIG. 2 shows an example of a combiner circuit for a Doherty PA. Such acombiner can be configured to provide moderate bandwidth performance. InFIG. 2, peaking amplifier signal and carrier amplifier signal are shownto be received from their respective collectors (not shown) and combinedso as to yield an output that can be provided to, for example, aduplexer. In FIG. 2, impedance values, as well as values of variouscapacitance and inductance elements, are examples; and it will beunderstood that other values can also be implemented.

The combiner 200 includes a first input port 211 (which may receive apeaking amplifier signal), a second input port 212 (which may receive acarrier amplifier signal), and an output port 213 that provides acombination of the signals received at the first input port 211 and thesecond input port 212.

The first input port 211 is coupled to a first node 211. The first node221 is further coupled to ground (via a first capacitor 241 and a thirdinductor 233) and to a second node 222 (via a first inductor 231). Thesecond node 222 is coupled to ground (via a second capacitor 242) and athird node 223 (via a second inductor 232).

The second input port 212 is coupled to a fourth node 224. The fourthnode is further coupled to ground (via a third capacitor 243 and a fifthinductor 235) and to a fifth node 225 (via a fourth inductor 234). Thefifth node 225 is coupled to ground (via a fourth capacitor 244) and thethird node 223 (via a fifth capacitor 245).

The output port 213 is coupled to a sixth node 226. The sixth node 226is further coupled to ground (via a sixth inductor 236) and the thirdnode 223 (via a sixth capacitor 246).

The first input port 211, second input port 212, the first capacitor241, the third inductor 233, the third capacitor 243, and the fifthinductor 235 may be implemented as an integrated passive device (IPD).In some embodiments, the components may be implemented on a single GaAsdie 270.

The presented impedance at the second node 222 and the fifth node 225may each be 25 Ohms. The presented impedance at the third node 223 maybe 12.5 Ohms.

FIG. 3 shows an example of a power splitter circuit for a Doherty PA.Such a splitter can be utilized with the example combiner of FIG. 2, andbe configured to provide moderate bandwidth performance. In FIG. 3, aninput radio-frequency (RF) signal is shown to be received at input 311and be split into two paths. The first path can be coupled to a peakingPA at the first output 312, and the second path can be coupled to acarrier PA at the second output 313. Along the first path lies aninductor 331 and along the second path lies a capacitor 341. In FIG. 3,values of various capacitance and inductance elements, are examples; andit will be understood that other values can also be implemented.

FIG. 4 shows an example of a power splitter 400 that can be utilized asthe divider 104 of FIG. 1. In FIG. 4, the power splitter 400 includes atransformer 450 with two coils positioned relative to each other. Thefirst coil can have interleaved windings that are coupled to each other,with one winding being coupled to an input 411 and the other windingbeing coupled to a first output 414. The second coil can haveinterleaved windings that are coupled to each other, with one windingbeing coupled to an isolation port 412 and the other winding beingcoupled to a second output 413.

The example of FIG. 4 can be configured as a quadrature splitter havingbroadband capability. Such a splitter can be configured as a semi-lumped90 degree power divider that can be implemented as IPD design for lowfrequencies and also as an integrated divider on GaAs die for higherfrequencies.

The power splitter 400 can further include capacitors 441, 442 couplingthe coils. In some embodiments, a first capacitor 441 is coupled betweenthe input 411 and the isolation port 412 and a second capacitor 442 iscoupled between the first output 413 and the second output 414.

With the foregoing configuration, power of an RF signal received at theinput port can be split into the two output ports 413, 414. Such splitsignals can be provided to the carrier amplifier and peaking amplifierof FIG. 1.

FIG. 5 shows an example of a power splitter 500 that can be utilized asthe divider 104 of FIG. 1. Additional details concerning such a powersplitter are described in U.S. patent application Ser. No. ______[Attorney Docket 75900-50074US], entitled SYSTEMS AND METHODS RELATED TOLINEAR AND EFFICIENT BROADBAND POWER AMPLIFIERS.

The example of FIG. 5 can be configured as a quadrature splitter havingbroadband capability. In some embodiments, such a splitter can beconfigured as a lumped 90 degree power divider that can be implementedas an SMT circuit for low frequencies, and also as an integrated (e.g.,IPD) divider on GaAs die for higher frequencies.

FIG. 6 shows an example of a combiner 600 that can be utilized as thecombiner 144 of FIG. 1. Additional details concerning such a combinerare described in U.S. patent application Ser. No. ______ [AttorneyDocket 75900-50074US], entitled SYSTEMS AND METHODS RELATED TO LINEARAND EFFICIENT BROADBAND POWER AMPLIFIERS.

The example of FIG. 6 can be implemented as an SMT circuit havingbroadband capability. In some embodiments, such a combiner can includepower combining and dynamic load pulling functionalities implementedwith use of a lumped balun.

FIG. 7 shows another example of a combiner 700 that can be utilized asthe combiner 144 of FIG. 1. Additional details concerning such acombiner are described in U.S. patent application Ser. No. ______[Attorney Docket 75900-50115US], entitled CIRCUITS, DEVICES AND METHODSRELATED TO COMBINERS FOR DOHERTY POWER AMPLIFIERS.

The example of FIG. 7 can be implemented as an IPD having broadbandcapability. In some embodiments, such a combiner can include powercombining and dynamic load pulling functionalities implemented with useof a semi-lumped 90 degree hybrid configuration.

Referring to FIG. 1, in some embodiments, each of the driver stage 116and the output stage 120 of the carrier amplifier 114 can be configuredto operate in a Class AB mode. Further, each of the driver stage 136 andthe output stage 140 of the peaking amplifier 134 can be configured tooperate in a Class B mode. For such configurations, bias circuits suchas those shown in FIGS. 9 and 10 can be utilized to bias the stages ofthe carrier amplifier 114 and peaking amplifier 134, respectively. Thus,the carrier amplifier 114 and the peaking amplifier 134 may operate indifferent biasing modes. Further, for each amplifier 114, 134, eachstage (116, 120 and 136, 140) may operate in different biasing modes.The different biasing modes can include Class A, Class B, Class AB,Class C, Class D, Class F, Class G, Class I, Class S, Class T, or anyother biasing mode.

FIG. 8 shows an example of a low headroom Class AB bias circuit that canbe utilized to provide a bias voltage (VBIAS) to a stage (driver 116 oroutput 120) of the carrier amplifier 114. Accordingly, the Class AB biascircuit can provide the biasing functionality of the bias circuit 118and/or the bias circuit 122 of FIG. 1. Appropriate selections oftransistors, diodes, capacitances and resistances can be implemented toaccommodate such driver and output stage functionalities. In someembodiments, the example bias circuit of FIG. 8 can be particularlysuitable for integration with external band gap references on CMOS orGaAs where low voltage headroom makes use of conventional 2xVbe biascircuits difficult. The bias circuit of FIG. 8 can include sufficientbandwidth at baseband frequencies to support broad band signals such asLTE.

FIG. 9 shows an example of a low headroom Class B bias circuit that canbe utilized to provide a bias voltage (VBIAS) to a stage (driver 136 oroutput 140) of the peaking amplifier 134. Accordingly, the Class B biascircuit can provide the biasing functionality of the bias circuit 138and/or the bias circuit 142 of FIG. 1. Appropriate selections oftransistors, diodes, capacitances and resistances can be implemented toaccommodate such driver and output stage functionalities.

FIG. 10 shows an example of a beneficial effect of utilizing a Class Bbiasing of the driver stage for the peaking amplifier (134 in FIG. 1).The graph 1000 of FIG. 10 includes plots of output stage current as afunction of output power for different configurations. For the carrieramplifier, the solid line 1011 is for a configuration where each of thedriver and output stages is biased in a Class B mode, while the dashedline 1011 is for a configuration with Class AB biasing of the driverstage and Class B biasing of the output stage. Similarly, for thepeaking amplifier, the solid line 1021 is for a configuration where eachof the driver and output stages is biased in a Class B mode, while thedashed line 1022 is for a configuration with Class AB biasing of thedriver stage and Class B biasing of the output stage. As shown in FIG.10, the use of Class B biasing in the driver stage in the peakingamplifier greatly reduces the current consumption of the output stage.However, the use of Class B biasing in the driver stage in the carrieramplifier slightly increases the current consumption of the outputstage.

FIG. 11 shows an example of a beneficial effect of utilizing a Class Bbiasing of the driver stage for the peaking amplifier (134 in FIG. 1).The graph 1100 of FIG. 11 includes plots of power-added efficiency (PAE)as a function of output power for different configurations. The solidline 1101 is for a configuration where each of the driver and outputstages of the peaking amplifier is biased in a Class B mode. The dashedline 1102 is for a configuration where the driver stage is biased in aClass AB mode, and the output stage is biased in a Class B mode. Thedash-dash line 1103 is for an equivalent non-Doherty amplifier biased ina Class AB mode. As shown in FIG. 11, the use of Class B biasing in thedriver stage in the peaking amplifier increases the PAE performancesignificantly.

FIG. 12 shows an example of linearization effect that can be obtained byintroducing a phase shift between the RF signals associated with thecarrier amplification and peaking amplification. Such a phase shift canbe introduced by, for example, the phase shift component 132 of FIG. 1.The graph 1200 of FIG. 12 includes plots of AM/AM (left vertical axis)and AM/PM (right vertical axis) as a function of output power. For theAM/AM plots 1211, 1212, FIG. 12 shows that the curve corresponding to aconfiguration with a phase shift has less AM/AM distortion, especiallyat higher output power, than a configuration without phase shift.Similarly, for the AM/PM plots 1221, 1222, FIG. 12 shows that the curvecorresponding to a configuration with a phase shift has less AM/PMdistortion, especially at higher output power, than a configurationwithout phase shift.

As described herein, power split into the carrier amplification path andthe peaking amplification path can be different. FIG. 13 shows anexample of linearization effect that can be obtained by introducing suchan uneven power split between the RF signals associated with the carrieramplification and peaking amplification. Such an uneven power split canbe introduced by or be facilitated by, for example, the attenuatorcomponent 112 of FIG. 1. The graph 1300 of FIG. 13 includes plots ofAM/AM (left vertical axis) and AM/PM (right vertical axis) as a functionof output power. For the AM/AM plots 1311, 1312, FIG. 13 shows that thecurve corresponding to a configuration with an uneven power split hasless AM/AM distortion, especially at higher output power, than aconfiguration with an even power split configuration. Similarly, for theAM/PM plots 1321, 1322, FIG. 13 shows that the curve corresponding to aconfiguration with an uneven power split has less AM/PM distortion,especially at mid to higher output power, than a configuration with aneven power split configuration.

FIG. 14 shows an example of combined linearization effect that can beobtained by a combination of the foregoing phase shift and uneven powersplit features described in reference to FIGS. 12 and 13. The graph 1400of FIG. 14 includes plots of gain (left vertical axis) and PAE (rightvertical axis) as a function of output power. In particular, line 1411shows the gain for a non-Doherty amplifier, line 1412 shows the gain fora Doherty amplifier without phase shift and even power split, and line1413 shows the gain for Doherty amplifier with phase shift and unevenpower split. Similarly, line 1421 shows the PAE for a non-Dohertyamplifier, line 1412 shows the PAE for a Doherty amplifier without phaseshift and even power split, and line 1413 shows the PAE for Dohertyamplifier with phase shift and uneven power split.

FIG. 14 shows that the linear load modulated amplifier (Doherty PA withphase shift and uneven power split) has a gain compression curve that isvery similar to that of a non-Doherty PA (e.g., Class AB/F amplifier).FIG. 14 also shows that the PAE of the linear load modulated amplifier(Doherty PA with phase shift and uneven power split) is only slightlyless (e.g., about 3% less at higher output power) than that of a classicnon-linear Doherty amplifier (Doherty PA with no linearization).

FIG. 15 shows plots of PAE (left vertical axis) and adjacent channelpower (ACP) (right vertical axis) at various operating frequencies for afront-end module (FEM) having a dual-band Doherty PA configured for LTEoperation, and an FEM having an average power tracking (APT) PA. FIG. 15shows that the PAE is generally higher, and the magnitude of ACP isgenerally lower, for the Doherty PA than the APT PA. In the exampleshown, the improvement is about 10%.

In some implementations, a device and/or a circuit having one or morefeatures described herein can be included in an RF device such as awireless device. Such a device and/or a circuit can be implementeddirectly in the wireless device, in a modular form as described herein,or in some combination thereof. In some embodiments, such a wirelessdevice can include, for example, a cellular phone, a smart-phone, ahand-held wireless device with or without phone functionality, awireless tablet, etc.

FIG. 16 schematically depicts an example wireless device 801 having oneor more advantageous features described herein. In the example, one ormore PAs 110 a-110 d collectively indicated as a PA architecture 101 caninclude one or more features as described herein. Such PAs canfacilitate, for example, multi-band operation of the wireless device801.

The PAs 110 a-110 d can receive their respective RF signals from atransceiver 810 that can be configured and operated to generate RFsignals to be amplified and transmitted, and to process receivedsignals. The transceiver 810 is shown to interact with a basebandsub-system 808 that is configured to provide conversion between dataand/or voice signals suitable for a user and RF signals suitable for thetransceiver 810. The transceiver 810 is also shown to be connected to apower management component 806 that is configured to manage power forthe operation of the wireless device 801. Such power management can alsocontrol operations of the baseband sub-system 808 and the PAs 110 a-110d.

The baseband sub-system 808 is shown to be connected to a user interface802 to facilitate various input and output of voice and/or data providedto and received from the user. The baseband sub-system 808 can also beconnected to a memory 404 that is configured to store data and/orinstructions to facilitate the operation of the wireless device 801,and/or to provide storage of information for the user.

In the example wireless device 801, outputs of the PAs 110 a-110 d areshown to be matched (via match circuits 820 a-820 d) and routed to anantenna 816 via their respective duplexers 812 a-812 d and aband-selection switch 814. The band-selection switch 814 can beconfigured to allow selection of an operating band. In some embodiments,each duplexer 812 can allow transmit and receive operations to beperformed simultaneously using a common antenna (e.g., 816). In FIG. 16,received signals are shown to be routed to “Rx” paths (not shown) thatcan include, for example, a low-noise amplifier (LNA).

A number of other wireless device configurations can utilize one or morefeatures described herein. For example, a wireless device does not needto be a multi-band device. In another example, a wireless device caninclude additional antennas such as diversity antenna, and additionalconnectivity features such as Wi-Fi, Bluetooth, and GPS.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled”, as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Additionally, the words “herein,” “above,” “below,” and words of similarimport, when used in this application, shall refer to this applicationas a whole and not to any particular portions of this application. Wherethe context permits, words in the above Description using the singularor plural number may also include the plural or singular numberrespectively. The word “or” in reference to a list of two or more items,that word covers all of the following interpretations of the word: anyof the items in the list, all of the items in the list, and anycombination of the items in the list.

The above detailed description of embodiments of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whileprocesses or blocks are presented in a given order, alternativeembodiments may perform routines having steps, or employ systems havingblocks, in a different order, and some processes or blocks may bedeleted, moved, added, subdivided, combined, and/or modified. Each ofthese processes or blocks may be implemented in a variety of differentways. Also, while processes or blocks are at times shown as beingperformed in series, these processes or blocks may instead be performedin parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

While some embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

What is claimed is:
 1. A power amplifier (PA) system comprising: aninput circuit configured to receive a radio-frequency (RF) signal andsplit the RF signal into a first portion and a second portion; a Dohertyamplifier circuit including a carrier amplifier coupled to the inputcircuit to receive the first portion and a peaking amplifier coupled tothe input circuit to receive the second portion, the first portion andthe second portion having different phases and different powers; and anoutput circuit coupled to the Doherty amplifier circuit, the outputcircuit configured to combine outputs of the carrier amplifier and thepeaking amplifier to yield an amplified RF signal.
 2. The PA system ofclaim 1 wherein the input circuit includes a phase-shifter configured tocause the first portion and the second portion to have different phases.3. The PA system of claim 2 wherein the phase-shifter and peakingamplifier are implemented in a peaking amplification path.
 4. The PAsystem of claim 1 wherein the first portion and second portion areout-of-phase by between 10 degrees and 20 degrees.
 5. The PA system ofclaim 1 wherein the different phases reduce at least one of AM/AMdistortion or AM/PM distortion as compared to equal phases.
 6. The PAsystem of claim 1 wherein the input circuit includes an attenuatorconfigured to cause the first portion and the second portion to havedifferent powers.
 7. The PA system of claim 6 wherein the attenuator andthe carrier amplifier are implemented in a carrier amplification path.8. The PA system of claim 1 wherein the different powers reduce at leastone of AM/AM distortion or AM/PM distortion as compared to equal powers.9. The PA system of claim 1 wherein the input circuit includes apre-driver amplifier.
 10. The PA system of claim 1 wherein the peakingamplifier includes a driver stage configured to operate in a firstbiasing mode and an output stage configured to operate in a firstbiasing mode.
 11. The PA system of claim 10 wherein the first biasingmode is a Class B biasing mode.
 12. The PA system of claim 11 whereinthe Class B biasing mode increases the PAE of the peaking amplifier ascompared to a Class AB biasing mode.
 13. The PA system of claim 10wherein the carrier amplifier includes a driver stage configured tooperate in a second biasing mode.
 14. The PA system of claim 13 whereinthe second biasing mode is a Class AB biasing mode.
 15. The PA system ofclaim 13 wherein the carrier amplifier further includes an output stageconfigured to operate in the first biasing mode.
 16. The PA system ofclaim 13 wherein the carrier amplifier further includes an output stageconfigured to operate in the second biasing mode.
 17. A power amplifier(PA) module comprising: a packaging substrate configured to receive aplurality of components; and a PA system implemented on the packagingsubstrate, the PA system including an input circuit configured toreceive a radio-frequency (RF) signal and split the RF signal into afirst portion and a second portion, a Doherty amplifier circuitincluding a carrier amplifier coupled to the input circuit to receivethe first portion and a peaking amplifier coupled to the input circuitto receive the second portion, the first portion and the second portionhaving different phases and different powers, and an output circuitcoupled to the Doherty amplifier circuit, the output circuit configuredto combine outputs of the carrier amplifier and the peaking amplifier toyield an amplified RF signal.
 18. The PA module of claim 17 wherein atleast one of the input circuit or the output circuit is implemented asan integrated passive device.
 19. The PA module of claim 17 wherein atleast one of the input circuit or the output circuit is implemented on asingle GaAs die.
 20. A wireless device comprising: a transceiverconfigured to generate a radio-frequency (RF) signal; a power amplifier(PA) module in communication with the transceiver, the PA moduleincluding an input circuit configured to receive the RF signal and splitthe RF signal into a first portion and a second portion, a Dohertyamplifier circuit including a carrier amplifier coupled to the inputcircuit to receive the first portion and a peaking amplifier coupled tothe input circuit to receive the second portion, the first portion andthe second portion having different phases and different powers, and anoutput circuit coupled to the Doherty amplifier circuit, the outputcircuit configured to combine outputs of the carrier amplifier and thepeaking amplifier to yield an amplified RF signal; and an antenna incommunication with the PA module, the antenna configured to facilitatetransmission of the amplified RF signal.